Some personal watercraft (PWC) is equipped with a supercharger which is one type of an auxiliary machine of an engine mounted therein. The supercharger is typically configured to be driven by a crankshaft of the engine via a belt and pulley mechanism.
Generally, a pulley attached to an input shaft of the supercharger is provided with a driving force disconnecting mechanism such as an electromagnetic clutch. The driving force disconnecting mechanism is aimed at protecting the supercharger from a fluctuation in an engine speed, which tends to increase when a propeller moves away from water surface, for example, the personal watercraft jumps out of the water surface, and to thereafter decrease when the watercraft lands in the water surface.
However, the electromagnetic clutch is required to be made of a magnetic material and thus is susceptible to corrosion because of sea water. Whereas the electromagnetic clutch may be subjected to rust-proof surface treatment, the surface treatment of at least a clutch surface may wear out when the clutch is turned on. For this reason, the electromagnetic clutch is not always suitable for use in the power damping mechanism of the input shaft of the auxiliary machine of the engine mounted in the personal watercraft.